1. Field of the Invention
The present invention relates generally to photovoltaic devices. The present invention relates more particularly to photovoltaic roofing products in which a photovoltaic element is joined to a roofing substrate.
2. Summary of the Related Art
The search for alternative sources of energy has been motivated by at least two factors. First, fossil fuels have become increasingly expensive due to increasing scarcity and unrest in areas rich in petroleum deposits. Second, there exists overwhelming concern about the effects of the combustion of fossil fuels on the environment due to factors such as air pollution (from NOx, hydrocarbons and ozone) and global warming (from CO2). In recent years, research and development attention has focused on harvesting energy from natural environmental sources such as wind, flowing water, and the sun. Of the three, the sun appears to be the most widely useful energy source across the continental United States; most locales get enough sunshine to make solar energy feasible.
Accordingly, there are now available components that convert light energy into electrical energy. Such “photovoltaic cells” are often made from semiconductor-type materials such as doped silicon in either single crystalline, polycrystalline, or amorphous form. The use of photovoltaic cells on roofs is becoming increasingly common, especially as device performance has improved. They can be used to provide at least a significant fraction of the electrical energy needed for a building's overall function; or they can be used to power one or more particular devices, such as exterior lighting systems.
Existing photovoltaic modules do not blend well aesthetically with conventional roofing materials. Photovoltaic materials tend to have a deep blue/purple/black color, which lends them increased solar absorptivity and therefore increased efficiency. Standard asphalt composite shingles, for example, are generally grey, black, green or brown in tone. Stone, wood and ceramic materials also have appearances quite different from that of photovoltaic materials. Moreover, many synthetic roofing materials (e.g., plastic tiles, shakes, slates and panels) are fabricated to appear like a more traditional material (e.g., stone, ceramic or wood). Accordingly, the contrast between photovoltaic materials and standard roofing materials can be quite dramatic.